ISLAMABAD, PAKISTAN - The top American commander in Afghanistan revealed Monday the size of U.S. troop force in the country has quietly been reduced by 2,000 over the last year, insisting remaining military personnel are still capable of reaching their stated objectives.

The revelation by Gen. Austin Scott Miller, means the number of residual U.S. force now stands at roughly 12,000 soldiers. They are tasked with fighting terrorist groups, including al-Qaida and Islamic State, as well as training, advising and assisting Afghan forces battling Taliban insurgents.

"Unbeknownst to the public as part of our optimization, over the last year... we have reduced our authorized strength by 2,000 here," Miller told a joint news conference with visiting U.S. Defense Secretary Mark Esper in Kabul.

"So, there is a constant look as a military commander to optimize the force here, and what it's based on is you understand the risks to the force, risks to the mission, and look at it in terms of capabilities," Gen Miller said. He was responding to comments Esper made a day earlier that even if the troop size is eventually reduced down to 8,600, it will not undermine the U.S. mission in Afghanistan.

The U.S. defense secretary arrived in the Afghan capital on an unannounced visit Sunday and held talks with Afghan President Ashraf Ghani, and met with U.S. service members.

Esper on Monday dismissed concerns that Washington could be preparing to stage an abrupt pull out from Afghanistan, as many see the U.S. military doing in northeastern Syria.

"We have a long standing commitment to our Afghan partners. We have invested billions upon billions of dollars. Both the Afghan people and the American people have sacrificed treasure and the lives of their soldiers," Esper noted.

A "virulent terrorist " threat is still facing the country, he said.

"So, all these things I think should reassure our Afghan allies and others that they should not misinterpret our actions in the recent week or so with regard to Syria and contrast that with Afghanistan," Esper stressed.

During his visit, the U.S. defense secretary also emphasized that a political agreement was "always the best way forward" with regard to next steps in Afghanistan.

His comments came days after U.S. chief peace negotiator Zalmay Khalilzad informally met with Afghan Taliban leaders in Pakistan, raising hopes the stalled dialogue might eventually resume to bring an end to the 18-year-old Afghan war.

U.S. President Donald Trump abruptly broke off the yearlong dialogue last month, just when the two adversaries had come close to signing a peace deal. He cited an uptick in Taliban attacks and the death of an American solider in a car bombing in Kabul that also killed 11 Afghan civilians.

Just before the collapse of the dialogue with the insurgent group, Khalilzad had said the U.S. was supposed to withdraw more than 5,000 troops from Afghanistan within the first five months of the signing of the draft deal he negotiated with the Taliban.

That would have reduced the size of the U.S. troop force to roughly around 8,600.

The Taliban has repeatedly called for American interlocutors to return to the negotiating table to conclude the agreement, insisting the document is just awaiting signatures from the two sides.

Also Sunday, a group of senior American lawmakers led by House Speaker Nancy Pelosi made a secret grip to the country.

Pelosi's office said in a statement Sunday her bipartisan delegation met President Ghani, the country's chief executive Abdullah Abdullah and civil society leaders, as well as U.S. military commanders. The delegation was able to briefly compare notes with Esper and was briefed by U.S. diplomats in Afghanistan on reconciliation efforts with Taliban insurgents.

Trump has in recent days repeatedly underscored the need for ending what he often refers to as America's "endless" foreign wars. He has made those comments particularly with reference to the Afghan conflict, which entered its 19th year this month.

Some analysts, like Michael Kugelman at the Willson Center in Washington are skeptical on whether U.S. assurances will help ease Afghan concerns.

"Trump's growing impatience with the war in Afghanistan is a major concern among Afghans, and the U.S. defense secretary's boilerplate comments about seeking an eventual settlement won't do much to ease those concerns. There's well-founded anxiety in Afghanistan that Trump may eventually withdraw before a peace deal is struck," Kugelman noted.

He says it is no secret that Trump wants to bring U.S. troops home and he has been "unwavering" in his sentiment.

"When he articulates this desire publicly, he not only underscores one of his few consistent positions- and one supported by many Americans - but he also reinforces the leverage enjoyed by the Taliban. President Trump is in a hurry to leave Afghanistan, and the insurgents have the luxury of waiting him out until the day that U.S. soldiers head for the exits," Kugelman cautioned.